Subject: Further sp4 clarifications

(This message is being sent to CPSC 215 Students and TA's)

(1) It is mandatory that all arithmetic in the map_pix.. function
    be done in the floating point domain.  You can achieve that
    by casting the first element in the expression to a double.

    e.g. (double) x / (proj->win...)

(2) The -1 correction needs to be applied to the "y" coordinate
    too.

(3) In Java and C++ class methods refer to class data elements
    directly by name without qualfication. So a statement such
    as

    fscanf(in,"%lf %lf",  &win_size_world[0], &win_size_world[1]);

    will work correctly in C++ if proj_t is a class and projection_init()
    is a class method.

    The C language has neither classes nor class methods!! Therefore
    any attempt to use a statement such as the one above will yield:

    projection.c:21: `win_size_world' undeclared (first use in this function)
    projection.c:21: (Each undeclared identifier is reported only once
    projection.c:21: for each function it appears in.)


    In C, EVERY reference to an element of a structure must be
    prefaced by xxx. or xxx-> where xxx represents the
    name of an instance of or a pointer to the structure
    of which win_size_world is a member!